TOOOFST -
The Pilots like many other tires, have "wear bars" in-between the tread groves. When the wear bars make contact with the ground surface area, it's an indication to replace your tires.
The biggest issue to be aware of is; <u>NOT</u> only how much tread is left your tires, but how long they've been on the vehicle. The Viper induces a good amount of torque load on the tires, the constant heat cycling (cold to hot ... cold) compromises traction by agitating the tire's compound. Throw a new set of tires on your car when age becomes a contributing factor, traction/handling will be much improved as well as safety as an added bonus.
Good Luck,
Doug